lecture 4 - visual overview

Question 1

what is the purpose of the visual cortex

Answer 1

processes visual information

Question 2

what is the purpose of the lateral geniculate nucleus

Answer 2

relay centre between the retina and visual cortex

Question 3

what does the ventral pathway tell us

Answer 3

what kind of stimulus

Question 4

what does the dorsal pathway tell us

Answer 4

where the stimulus is

Question 5

what is the role of the pupil

Answer 5

regulates the amount of light falling on the retina

Question 6

what is the role of the lens

Answer 6

focuses the image on the fovea

Question 7

what is the fovea

Answer 7

the part of the retina with the highest visual acuity (one connection for each neuron)

Question 8

what is the structure of the retina from the light source inwards

Answer 8

ganglion cells
inner plexiform
amacrine cells
bipolar cells
horizontal cells
outer plexiform
photoreceptors

Question 9

which cells in the retina are excitatory (release glutamate)

Answer 9

ganglion
bipolar
photoreceptors

Question 10

which cells in the retina are inhibitory

Answer 10

horizontal
amacrine

Question 11

at which light conditions are rod cells activated

Answer 11

dim light

Question 12

at which light conditions are cone cells activated

Answer 12

bright light

Question 13

does hyperpolarisation or depolarisation occur in photoreceptors?

Answer 13

hyperpolarisation

Question 14

does hyperpolarisation or depolarisation occur in bipolar cells

Answer 14

both, depends on which type

Question 15

describe phototransduction

Answer 15

rhodopsin activated by light
stimulates transducin to become transducin GTP
alpha subunit activates phosphodiesterase which reduces cGMP levels
hyperpolarisation

Question 16

where does phototransduction occur

Answer 16

photoreceptors

Question 17

what happens to glutamate release when photoreceptors are hyperpolarised due to light

Answer 17

it is decreased

Question 18

describe the main differences between ON and OFF bipolar cells

Answer 18

ON- depolarise with light, metabotrophic glutamate receptors, removal of cGMP not required for ion channel closure

OFF- hyperpolarise with light- use AMPA receptors

Question 19

where do ON bipolar cells send their projections to

Answer 19

lower IPL (closer to ganglion cell layer)

Question 20

where do OFF bipolar cells send their projections to

Answer 20

upper IPL

Question 21

what does a receptive field mean

Answer 21

retinal ganglion cells will only fire APs when specific areas are illuminated

Question 22

does phototransduction occur in the outer or inner segment of photoreceptors

Answer 22

outer

Question 23

what is centre- surround organisation and where does it occur

Answer 23

where the 2 different regions of a cell(inner and outer) have opposite polarities

occurs in bipolar cells and ganglion cells

Question 24

how does centre-surround organisation happen

Answer 24

direct photoreceptors(in middle) will activate bipolar cells

peripheral photoreceptors will active bipolar cells via horizontal cells
these horizontal cells reverse the signal as they are inhibitory

Question 25

what is the difference in effect of receptive fields of ganglion cells and bipolar cells, and why

Answer 25

ganglion cells generate action potentials bipolar cells generate graded potentials ganglion cells have to send signals over long distances whereas bipolar cells dont

Question 26

describe the firing of OFF ganglion cells

Answer 26

non when light hits centre more when light hits edge none when light hits both

Question 27

describe the firing of ON ganglion cells

Answer 27

more when light hits centre non when light hits edge non when light hits both

Question 28

what are the 2 types of ganglion cell

Answer 28

parvocellular magnocellular

Question 29

what are the key differences between parvocellular and magnocellular cells

Answer 29

P- small dendritic tree M- large P-respond to colour M-respond to motion P- produce APs M- produce quick bursts of energy P- low sensitivity M- high sensitivity

Question 30

what is the main cell type of the retina

Answer 30

rod

Question 31

what is the synapse between in the outer plexiform layer of the retina

Answer 31

photoreceptors and bipolar/horizontal cells

Question 32

which cells is the synapse between in the inner plexiform layer

Answer 32

bipolar and ganglion/amacrine amacrine and ganglion/other amacrine

Question 33

which bipolar cell responds less when stimulated by light and why

Answer 33

OFF they are located in the upper plexiform layer so further from light source

Question 34

why do ganglion cells respond well to edges of objects

Answer 34

due to the fact that they generate no response when light hits both the centre and surrounding, need a dramatic change